1. Field of the Invention
The invention relates generally to hair styling devices and in particular to handheld appliances used for the curling and setting of hair.
2. Description of the Prior Art
Handheld heatable curling irons and curling brushes are styling devices well-known in the art for setting curls in hair. The term "curling iron" is used generically here and in the art to mean devices as hereinafter described generally comprising a handle and a cylindrical hair winding portion or barrel or tube attached thereto for having hair wound thereon. While the term "curling iron" is used herein, it will be understood that the invention is equally applicable to curling brushes. The barrels are often made of aluminum or some other lightweight metal (having good thermal conductivity characteristics) and are provided with some means for heating the barrel. The barrels may be covered with some flocked material to facilitate gripping the hair and may be provided with bristles to to form a brush. The heating means of prior art curling irons may comprise an electrical resistance heater within the barrel or a self-contained catalytic heater, and in some devices the use of a temperature regulating means (for example, a PTC resistor) controls the temperature of the barrel. Selected hair tresses are wound around the barrel and heat is transferred by conduction from the heated barrel to the hair.
All known curling irons require hair tresses to be wound about the heated barrel and, therefore, the outer layers of hair are insulated from contact with the barrel surface by the inner layers. Regardless of the manner in which the barrel is heated, it is apparent that known prior art curling irons are conduction heating devices and have a tendency to heat and dry the inner layers of a hair tress before the outer layers. This often results in the user excessively heating and drying and therefore possibly damaging a portion of each tress in order to achieve the desired temperature for the outer layers.
Accordingly there is a need for a curling iron that can provide more uniform heating of hair. It has been found that irradiation of hair with electromagnetic radiation of a predetermined band in the infrared range achieves a desirable degree of uniform heating. Since the hair is randomly wound about the barrel of the curling iron with spaces between adjacent strands, radiant heating provides better energy transfer to the hair throughout the tress. The spacing between the inner strands permits the infrared radiation to penetrate through the hair tress to the outer layers which are then heated by the radiation as well as by conduction of heat from adjacent hair strands.
The use of infrared radiation of a predetermined wavelength on the order of 1 to 7 microns is known in bonnet-type hair dryers. Such a system is shown, for example, in French Pat. No. 1,150,093. Other bonnet-type hair dryers using infrared radiation are shown in U.S. Pat. Nos. 3,972,126, 4,259,566, 4,256,127 and 4,292,985. However, none of these prior art patents disclose the use of an infrared radiation source in a curling iron for the setting of curls and none of these patents disclose a handheld device. U.S. Pat. Nos. 4,323,761 and 4,263,500, assigned to the assignee hereof, do disclose handheld, radiant heat hair dryers using an infrared radiator and a fan for blowing air on the hair, however, neither of these devices are suitable for use in a curling iron.
Additional disadvantages of prior art curling irons is that they are very hot to the touch when in use (on the order of 140.degree. F.) and retain this high temperature whether they are curling hair or merely waiting to be used, thereby producing some risk of injury to the user. Additionally, because of the resistive or catalytic heating elements and the transfer of heat energy by conduction, there is a rather long warm-up period required before prior art irons are ready for use. For example, a catalytic butane curling iron has been found to require on the order of 4 to 5 minutes to reach operating temperature. A unit utilizing a positive temperature coefficient (PTC) resistance heater requires on the order of 7 to 8 minutes and a "rope" heater on the order of 12 minutes.
Another disadvantage of prior art conduction curling irons is the fact that they do indeed retain whatever heat is transferred to the barrel for a considerable time. It is well known that better curls may be set in hair if the hair can be cooled while it is being set in the desired position. Since prior art conduction curling irons remain on once they are turned on, they must be removed from one hair tress while still hot so that the iron may be used to set another hair tress. Consequently, each hair tress must be allowed to cool in a relatively uncurled position since the curl starts to unwind as soon as the iron is removed.
Accordingly it is an object of this invention to provide a curling iron capable of heating and curling hair through radiation of infrared energy.
It is another object of this invention to provide a curling iron having a relatively cool barrel temperature at times when the iron is not on and operatively engaged with a hair tress.
It is another object of this invention to provide a curling iron which reaches operating temperature relatively quickly, on the order of seconds as opposed to minutes, so that it may be turned on for the curling of each hair tress and turned off after the curling of each hair tress.
It is another object of this invention to provide a curling iron for the radiation heating of hair to a predetermined temperature.